MB-9321 Use leader_activities for graceful failover.
MB-9321 Use leader_activities for graceful failover.

Change-Id: Ie52941a7481ae937111f999227259fa1abe270bd
Reviewed-on: http://review.couchbase.org/88648
Tested-by: Aliaksey Artamonau <ce14b1c16e0fd654f926118eb8addbec5aff4ffa@couchbase.com>
Reviewed-by: Aliaksey Artamonau <ce14b1c16e0fd654f926118eb8addbec5aff4ffa@couchbase.com>

membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server